Flexural-extensional electromechanical transducer



ct. 4, 1966 w. J. ToULls 3,277,433

FLEXURAL-EXTENSIONAL ELECTROMECHANICAL TRANSDUCER Filed Oct. L7, 1965 5Sheets-Sheet 1 WILL/AM J TOUL/S arroRn/ys W. J. TOULIS FLEXURAL-EXTENSIONAL ELECTROMECHANI CAL TRANSDUCER 5 Sheets-Sheet 2 Filed OCC, 1.7,1965 INVENTOR.

W/LL /M J. TOUL/S C' 4, 1966 w. J. ToULls 3,277,433

FLEXURAL-EXTENSIONAL ELECTROMECHANICAL TRANSDUCER Filed 001;. 1.7, 19635 Sheeis-Sheet 3 INVENTOR. W/LL /A M J. TOULS d www ATTO/VEYS 3,277,433FlLEXlURAlJ-EXTENSHQNAL ELECTRO- MECHANICAL TRANSDUCER William ll.Toulis, 1100 E. Broad St., Columbus, Ohio Filed (9ct. 17, 1963, Ser. No.317,097 3 Claims. (Cl. 340-8) The invention described herein may bemanufactured and used by or for the Government of the United States ofAmerica for governmental purposes without the payment of any royaltiesthereon or therefor.

The present. invention relatesV to an electromechanical transduceradapted to detect or generate and radiate sound in fluid media and moreparticularly to such a transducer having a diaphragm which operates inthe flexural mode of vibration, a driver (for vibrating said diaphragm)which operates in the extensional mode of vibration, and in which thediaphragm and driver are linked together thr-ough a mechanicaltransformer, in order to couple more efficiently the vibrational energytransfer between the driver and the diaphragm.

Among Objects of importance of the present invention are:

To provide preferably a very-nearly-omnidirectional electroacoustictransducer.

To provide .a transducer having low vibrational mass for broad frequencyresponse.

To provide a transducer which may have high electromechanical conversioneiciency so that the radiated power may be large over a broad band offrequencies.

To provide a transducer employing a piezoelectric ceramic driver wherethe power output is not limited by th-e tensile strength of the ceramicmaterial of which the driver is composed.

To provide a composite transducer comprising a given number ofindividual diaphragm-driver sections whose cooperative action gives thetransducer an improved frequency response and power output.

Other objects and many of the attendant advantages of this inventionwill be readily appreciated as the same becomes better understood byreference to the following detailed description when considered inconjunction with the accompanying drawing in which:

FIG. 1 is the transducer assembly, shown partly in section;

FIG. 2 is an exploded view of the transducer seen in FIG. 1 to show withgreater clarity the majority of the various components which go into theassembled transducer;

FIG. 3A shows one of the identical diaphragm-driver sections (of thetransducer) utilizing a (slightly modified) compliant tube shapestructure for the diaphragm (ie, radiating surface);

FIG. 3B shows a like diaphragm-driver section with a modified(honeycombed) diaphragm;

FIG. 3C shows a like diaphragm-driver section with another modificationof the diaphragm (i.e., a mass loaded diaphragm); and

FlG. 3D shows a transducer section reflecting the use of a standardcompliant tube shape diaphragm and spacer, in contradistinction to theFIGS. 3A-3C which show a transducer section wherein the compliant tubeform has been slightly modified to enable it to be used as a radiatingsurface (diaphragm) without the need for spacers FlG. 4 shows inperspective details of one transducer section embodying this invention.

The principal portion of the transducer 11 is a series ofsubstantially-identically constructed sections 12. FIG. 3(A-D) portraysa preferred embodiment of one of these sections 12. Each of thesesections 12 consists essen- Patented Oct. 4, 1966 tially of a diaphragm13 which is adapted to undergo flexural vibration to transmit sound intothe fluid medium in which the transducer is immersed and a driver 14.The driver 14, mounted in thrust-transmitting relationship withdiaphragm 13, is adapted to operate in the longitudinal (extensional)mode of vibration to impart to its diaphragm 13 the desired flexuralvibrational motions.

The diaphragm 13 is essentially a section of compliant tubing, astructure which is defined at length in the inventors issued Patent No.3,087,138, and in the inventors issued Patent No. 3,021,504. Aluminum isa representative material for this diaphragm 13. In the preferredembodiment shown here an elliptically-shaped compliant tube, of aluminumor like material, is employed for the diaphragm. The diaphragm may besolid in structure (FIG. 3A) or it may be honeycombed (i.e., madelongitudinally perforate) as seen in FIG. 3B, the latter structureserving to produce a diaphragm of reduced density. The perforations 16(shown in the FIG. 3B diaphragm embodiment) may extend throughout thelongitudinal length of this diaphragm 13. The density of the diaphragm13 may also be increased (rather than decreased) by the addition to thenormal solid diaphragm (unperforated) of an additional loading charge. Amass loaded diaphragm is shown in the FIG. 3C diaphragm embodiment wherelead bars 17 are fixedly secured to the inner surface of the diaphragmat both sides there-of as shown. These lead bars 17 are preferablymounted in opposing center balancing positions at opposite sides of thediaphragm 13, with their respective longitudinally-running center lineslying along the plane of symmetry defined by the various minor axes ofmultiple cross sections of the diaphragm 13 and preferably these bars 17run the full longitudinal length of the diaphragm 13. The variations ofthe diaphragm 13, as just described, are utilized as methods for varyingthe mechanical Q of the transducer 11 which is composed of thesesections 12. The mechanical Q of a transducer increases with thedensity, the thickness, mass loading, degree of curvature or stiffnessof its diaphragm. This mechanical Q or sharpness of resonance of avibrating structure is highly significant in terms of the electricalefficiency, acoustic power output and effective frequency bandwidth. Ahigh mechanical Q leads to high efficiency and power output, but at asacrifice in usable bandwidth. A low mechanical Q, on the other hand,improves usable bandwidth at the expense of efliciency and power output.Use of a honeycomb structure diaphragm (FIG. 3B) conveys the advantagesof a low mechanical Q (improved frequency response). On the other hand,mass loading of the diaphragm (FIG. 3C) such as with lead bars 17improves the efficiency and power output of the transducer, at thesacrifice of usable bandwidth.

The construction of the driver 14 for each of the sections 12 is thesame regardless of whether a solid, or honeycombed, or mass loadeddiaphragm is employed. The driver 14, as shown, is a ceramic sandwicdriver structure which consists principally of a stack of piezoelectricceramic plates 18. It is well known that certain materials undergomechanical deformation when various voltages are applied across them.This effect, which can properly be described as the converse of thewell-known piezoelectric effect, has been found applicable to variouspolycrystalline ceramics whose most widely known member is probablybarium titanate (BaTiOg), which, when pre-polarized by the applicationof a sufficiently strong unidirectional field, serves as an excellenttransducing element. An illustrative reference on such a barium titanateceramic is U.S. Patent No. 2,486,560 to Grey. It has been found that,for the application herein, the lead zirconate titanate ceramic 3 (whichis disclosed in U.S. Patent No. 2,708,244 to Jaffe) is particularlyappropriate.

The maximum power output from a transducer employing a ceramic drivermay depend to a large extent on the degree of internal heat dissipationwithin the piezoceramic, the ability to dissipate heat rapidly and theduty cycle during normal opeartion. When the duty cycle is high and heatdissipation appreciable, the maximum power output (of the transducer)will be limited by the build-up in temperature within the ceramicdriver. Because the thermal conductivity of ceramics is low, thepiezoelectric ceramic comprising the driver 14 is constructed of thinpiezoceramic plates 18 in the configuration of an elongate stack, asseen in the various figures of the drawing. Each of these ceramic plates18 is plated with silver on two sides first (and preferably on the sidesto be bonded) in order to serve as electrodes to polarize and also todrive the stack electrically. These ceramic plates 18 are supplementedby a series of heat-dissipating members 19 each of which consists of twohorizontallyextending metallic (i.e. copper) inserts 21 and avertically-extending fine-wire mesh member 22 which links the metallicinserts 21. With the metallic (preferably copper) inserts 21 sandwichedin-between adjacent ceramic plates 18, heat originating in the ceramicplates 18 on both sides of a metallic insert 21 will be conducted awayto the fine-wire mesh member 22 from which this heat will thendissipate.

Heat dissipating members 19 also act as part of the electrical systemwhich actuates the various ceramic plates 18 to cause the driver 14 tovibrate in longitudinal mode in response to the actuating electricalsignal. It will be noted, as seen especially in FIGS. 3A-3D that eachsuccessive ceramic plate 18 is oppositely polarized from the nextpreceding ceramic plate. The drawing figures portray, with arrows, theinherent polarization of the various ceramic plates. With the individualheat dissipating members 19 embracing, by their metallic inserts 21, apair of successive, oppositely-polarized ceramic plates 18, bystaggering the heat dissipating members 19 which respectively appear tothe left and to the right of the stack of ceramic plates (see FIGS.3A-D) these heat dissipating members 19 also serve aselectricity-conducting electrodes for actuating the ceramic plates 18.Each of the metallic inserts 21 is preferably co-extensive in area withthe ceramic plate surfaces between which it is sandwiched so as topresent a uniform and mechanically balanced surface to each ceramicplate 18. With heat dissipating members 19 positioned in a staggeredseries with respect to the stack of ceramic plates 18, there will beformed a vertical row of fine-wire mesh members 22 to the right of theceramic-plate stack and a like vertical row of fine-wire mesh members 22to the left of the ceramic-plate stack. A right-hand bus bar 23 issecured in an electrically-conductive connection to the right-handvertical row of mesh members 22 and a left-hand bus bar 24 is connectedin like fashion to the left-hand vertical row of these mesh members 22.With the bus bar 23 connected to the one polarity of the actuatingelectrical signal and the other bus bar 24 connected to the otherpolarity of the actuating electrical signal as appropriate for the givenpolarization of the various ceramic plates 18, the driver 14 (composedof these ceramic plates 18) will vibrate in the longitudinal mode ofvibration to impart iiexural vibratile movement to the diaphragm 13.

Located in the stack of ceramic plates 18 which are maintained inrectilinear stack conformation by appropriate conventional bonding are apair of steel plates 26, each of which is substantially co-extensivewith the ceramic plates of the stack. For the majority of sections 12 oftransducer 11 each steel plate 26 is equipped at one end with a maleprong 27 and at its opposite end with a female opening 28 which isadapted to accommodate a like prong fitted to the steel plate 26 of anadjacent ceramic-plate stack when proximate sections 12 are fittedtogether to form the assembled transducer (the joining together of thevarious sections 12 of the transducer 11 will be dwelled upon infra).These steel plates 26 act both as appropriate spacers in theceramic-plate stack and as a means for securing together variousproximally-located drivers 14 of the transducer.

The piezoceramic driver of this invention need not be of the sandwichconstruction portrayed herein. This piezoceramic driver 14 may be simplyan integral, uniform piezo-driver with silver electrodes on appropriateoutside surfaces thereof, but preferably it is of the compositesandwich-like construction defined herein, which is considerably moredesirable (than the integral, uniform piezo-driver) for attainingmaximum output and bandwidth with the transducer. Various other of thenovel features of the transducer defined herein can be employed withdrivers other than piezoelectric ceramic drivers, such asmagnetostrictive drivers, for example.

Located at the respective vertical extrem-ities of the driver stack ofceramic plates are a pair of plastic sheet insulators 29 in compressedposition between the vertical ends of the stack of ceramic plates 18 andthe adjacent portion of the diaphragm 13 which is formed to accommodatethe driver `14 in a tightly-h-olding fit, The conventional complianttube-shape structure which goes to form the diaphragm 13 may be modifiedas seen in FIGS. 3A-3C, to form the driver-.abutting portion 31 whichcontacts plastic sheet insulator 29. On the other hand, if an unmodifiedelliptically-shaped complaint tube is employed it will be necessary toinclude, for mechanical reasons, intermediate plastic sheet insulator 29and the compliant tube 3-2, a spacer 33 (see FIG. 3D). Insulators 29which are It-o provide electrical insulation between the driver -1'4 andthe diaphragm 13 and the spacers 3=3 (when employed) are preferablyformed of as stiff a material as possible in order to minimizedecoupling between the driver 114 and the diaphragm 13.

One of the limiting factors present when piezoceramic drivers areemployed is the propensity for such drivers to fracture when employedfor high acoustic power output. "Bhe yield strength of piezoceramics`while in tension has been found to be only in the order of LOCO-4,000lbs./ ing. The stresses induced by electrical forces in the ceramic arecomparable and definitely much higher if the maximum acoustic out-put isto be limited by internal heating. Inasmuch as the compressive strength,however, of piezoceramics is known to be greater than 20,000 lbs/in?,the use of compressive prestress on a piezoceramic driver logicallysuggested itself as a way to eliminate fracture in the piezoceramic athigh power output. The use of biasing stress to prestress the ceramicplates 18 is employed in the transducer 11 so that high acoustic powermay be radiated by the transducer without danger of 'fracture of theceramic. This prestress is mechanically achieved herein simply byforcing inwardly the two vertically extending walls of diaphragm 13 andsliding the ceramic-plate 118 stack, as supplemented by the endinsulators 29, into place, as shown, after the proper dimensions andforces are selected to yield the desired degree of (compressional)prestress. When the vertically-extending walls of diaphragm 13 areforced inwardly to enlarge the natural vertical inside-dimension of thisdiaphragm 13 so that it will be able to accommodate a ceramic driverwhich is longitudinally-oversized with respect to the natural verticalinside dimension (of the diaphragm) and the positive deforming forceremoved from the diaphragm 13 .after ythe ceramic driver has beeninserted into operative position therewithin, the tendency -of thediaphragm 13 to seek its natural (undeformed) shape is the source of thecompressive bias for the ceramic-plate stack. The resulting prestressserves to prevent fracture of the ceramic material of the driver 14. Theuse of mechanical prestress to improve the yield strength ofpiezoceramic drivers has been employed previously, as seen for examplein the U.S. Patent No. 2,930,912 ent-itled Composite ElectromechanicalTransducer, and issued to H. B. Miller. In the Miller patent which, likethe present invention, employs a stack of ceramic plates in its driver,a plurality of individual stiff rods are used to put and keep undercompressive bias the stacked piezoceramic plates of the driver. The modeof effecting this compressive bias (prestressing) herein represents animprovement over that employing a plurality of stilinv rods. In themultiple rod method there is the significant problem of getting equalstress on the ceramic driver 14. A lack of equal stress makes theceramic liable to buckling and/or chipping. Here the compressive biasplaced upon the ceramic driver 14 by diaphragm 13 ensures theapplication of equal stress thereto. Multiple stiff-rod biasing of theceramic driver also producesV an incapacitating or degrading factor onthe effective electromechanical coupling factor for the transducerbecause of the stiffness of the rods, that is, it produ-ces a clampingaction on the ceramic driver to limit its vibratory motion. Here, on theother hand, the biasing action does not limi-t the vibratile motion ofthe ceramic driver because the biasing structure (Le. diaphragm) ismechanically resonant at the frequency of operation of the transducer.(The dimensions of the diaphragm 13 herein are such that this diaphragm13 is equally mass and stiffness controlled at optimum operatingfrequency, which is generally the resonant frequency. (Stiflness as usedhere is equatable with elastic resistance t-o change of dimension andmass, as employed here, with inertive resistance to change of motion.))Another distinction between the presetting bias action here and themultiple rod bias action (such as in the Miller patent) is that in themultiple rod biasing the rods vibrate in the extensional or longitudinalmode of vibration whereas here the compressing (bias) member (diaphragm13) vibrates in the flexural mode of vibration. This flexural mode ofvibration is much more amenable to resonance operation, i.e.,driver-compressing diaphragm 13 can be made to resonate with a feasibledimension requirement for the diaphragm. Compressing rods, on the otherhand, in order to be able to resonate, would ordinarily be beyondpracticable limits in length. The ability of the compressing member toattain resonance enables the transducer to achieve greater power outputand efiicieny.

Looking now to the transducer 11 as an assembled unit whose mainoperative portions are the various sections 12, FIG. l shows theassembled transducer partly in sectional view and FIG. 2 shows inexploded view the various main portions which go to make up theassembled transducer. Proximate transducer sections 12 are mechanicallyjoined together by the union of complementary male and female connectionmembers. The male prongs 27 extending from the steel plates 26 of one ofthe transducer section 11 are complementarily insertable into matingopenings 28 formed in the opposite side of steel plates 26 of the nextadjacent transducer section 12, to hold adjoining sections 12 linkedtogether. In like fashion the diap'hragms 13 of adjacent sections 12 areprovided with complementary prongs 34 and openings 36 which matetogether. Intermediate proximate sections 12 of lthe transducer 11 thereis a rubber gasket 37 which serves to develop, in conjunction with thecompressive pressure (effected in a manner to be described infra) uponit by each of the proximate sections 12, a liquidproof seal betweenthese proximate sections 12.

The first and last sections 12 of the series of sections 12 which makeup the complete transducer diaphragm are variously designated herein as12 and 12 respectively. The rst section 12 may not have operative needfor the openings 28 in its steel plates 2d and the last section 12 maynot have prongs 27 (on its steel plates 26) or prongs 34 (on itsdiaphragm 13). The respective ends of the assembled series of sections12 are closed off by the respective closure plates 33 and 39, each ofwhich has a rubber gasket 40 inserted between it and the abuttingsection 12. These closure plates 38 and 39 are appropriately bored toform holes 41 which receive a series of tie-rods 42 which, inconjunction with nuts 43 fastened to their threaded ends, serve both tohold the transducer sections 12 and their intervening gaskets 37 in atight union and to maintain closure plates 38 and 39 in tight, closingposition to seal off the ends of the transducer as well as serving toprevent the closure plates 38 and 39 from shifting laterally withrespect to the series of joined transducer sections 12.

One of the closure plates (here shown as closure plate 38) is providedwith a liquid-tight electrical coupling member 44 which has twoexternally located prongs 46 and 47 adapted to link to an external lead48. The complementary internally-located contact members 49 and 51 ofthis electrical coupling member 44 are electrically connected to tworespective leads S2 and 53. The first of these leads, lead 52, passesfrom the electrical coupling member 44 to interconnect, in seriesfashion, each right hand bus bar 23 of the various transducer sections12 t0 the one polarity-actuated portion of electrical coupling member 44and the other of these leads, lead 53, acts to electrically link theleft-hand bus bars 24 of the respective transducer sections 12 to theother polarity-actuated portion of the electrical coupling member 44. Itis in this fashion that the electrical actuating sign-al is carried tothe various drivers 14 of each of the sections 12 of the transducer 11.The overall diaphragm of the transducer 11 is comprised of the series ofsection diaphragms 13 and by way of the extensional vibratory movementof each of the section drivers 14, which all operate in phase with eachother, the overall transducer diaphragm is driven in flexural vibratilemovement by the actuating signal brought to the transducer 11 by theexternal electrical lead 48.

Depending upon the depth in the liquid medium at which the transducer 11is to be employed, the chamber, formed by the closed-off series ofsections 12 and containing the series of drivers 14, is either leftfilled with air or is oil filled or is filled with an appropriatepressurerelease material such as corprene, for example, (practices whichare conventional). An appropriate oil is silicone fluid. It must beborne in mind that the oil used must be of a character to preventelectrical arcing between the silver electrodes of the various drivers14 or between the ceramic plate-s 18 themselves.

The transducer 11, just described, is potentially characterized withhigh electromechanical efficiency and high power output along with atransmission capacity over a broad range of frequencies. For maximumpower output and efficiency it should preferably be operated nearmechanical resonance. In its usual dimensions it is very nearlyomnidirectional in radiation pattern. The general rule for determiningwhether a transducer is (selectively) directive, or not, in itsradiation pattern is that when the dimensions of the radiating surfaceof the transducer are small compared to the Wave-length of sound in theenveloping sound-propagating medium, such a transducer does not havedirectivity, i.e., its radiation pattern is omnidirectional incharacter. Directivity may be obtained with such transducers, whendesired, by arranging multiple such transducers in arrays or employingthem in conjunction with acoustic lenses or reectors. The mating of theextensional and exural modes of vibration, as achieved in thistransducer, produces a more effective transducer as it yields highacoustic output and desirable electro-acoustic characteristics with amuch smaller transducer than has been used previously. In thisextensionalexural transducer substantially all of the structure makingup the transducer is dynamic For example, in addition to serving as aradiating surface, as a mechanical transformer and as a prestressingagent for the piezoceramic, the diaphragm itself acts as the mainportion of the external-liquid-medlum-excluding container with no needfor the use of such structure as the conventional rubber boot whichoften serves as container and which presents the disadvantage of tendingto dampen the dynamics of the transducer operation. The simplicity ofsuch a transducer where the diaphragm also serves as theliquid-precluding envelope is patent. As noted supra, the character ofthe transducer diaphragm can be varied readily to give either increasedpower output and electroacoustic eiiiciency or greater frequencybandwidth, as desired. With its prestressed ceramic drivers it is ableto attain significantly high power output.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is intended to coverall changes and moditications of the embodiments set forth herein whichdo not constitute departures from the spirit and scope of thisinvention.

What is claimed is:

l. A composite electromechanical transducer, adapted to transmit ordetect sound in a liquid medium, and herein defined in terms of itssound transmission operation comprising in combination:

a plurality of open-ended tubular diaphragm members of identicalnon-circular cross-sections, each of said tubular diaphragm membersbeing adapted to vibrate in the tiexural mode of vibration fortransmitting sound into said liquid medium and said plurality of tubulardiaphragm members being arranged in a linear series whereby saiddiaphragm members form an integrally-operative tubularsound-transmitting means adapted to transmit sound into said liquidmedium;

electrically-actuable electromechanical converter means,

individual to and disposed within each of said diaphragm members inthrust-transmitting relationship therewith and vibratile in thelongitudinal mode of vibration in response to an actuating uctuatingelectrical signal, for driving its associated diaphragm member intiexural vibratile movement in response to said fluctuating electricalsignal;

closure means, connected to each end of said tubular sound-transmittingmeans, for closing off said tubular sound-transmitting means from saidliquid medium;

multiple sealing means for ensuring a liquid-proof connection betweenthe adjacent diaphragm members;

electrically-conductive actuating means, connected to each of saidelectromechanical converter means and adapted to connect to an externalelectrical lead bearing said iiuctu-ating electrical signs;

restraining means, connected to said closure means, for holding andmaintaining said closure means, said plurality of diaphragm members andsaid sealing means in assembled cooperation relationship with respect toeach other;

said converter mean-s each comprising:

a stack of electromechanically-active elements each of which is adaptedto alternately expand and contract along the longitudinal axis of saidstack in response to the application to said electromechanically-activeelements of an electric signal of iiuctuating intensity, thelongitudinal ends of said stack being in thrust-transmittingrelationship with its associated diaphragm member;

electrode means, operatively interconnecting each of `saidelectromechanically-active elements to said electrically-conductiveactuating means for bringing each of said electromechanically-activeelements under the operative influence of the actuating fluctuatingelectrical signal carried by said electrically-conductive actuatingmeans;

insulator means, intermediate the respective longitudinal ends of saidstack of electromechanically-active elements and the diaphragm memberassociated therewith, for electrically insulating said stack ofelectromechanically-active elements from said associated diaphragmmember; and

heat dissipating means, connected to each of theelectromechanically-active elements in said stack for conducting heataway from said electromechanically-active elements, said heat-dissipating means, in part, consisting of wire meslrlike structure foraccelerating the dissipation of heat away from saidelectromechanically-active elements.

2. A composite electromechanical transducer comprising in combination:

a plurality of open-ended tubular diaphragm members of identicalnon-circular cross-section, said diaphragm members being substantiallyellipitical in general cross-sectional configuration, each diaphragmmember being adapted to vibrate in the tiexural mode of vibration fortransmitting sound into water and said plurality of tubular membersbeing arranged in linear series;

electrically-actuable electromechanical converter means individual toand disposed within each of said diaphragm members in thrusttransmitting relationship;

each electromechanical converter means being longitudinally elongate anddisposed within its associated elliptical tubular diaphragm member withthe longitudinal axis of said converter means lying within the plane ofsymmetry deiined by the major axes of the cross-section of saiddiaphragm member and with the longitudinal axes of said converter meansperpendicular to the plane of symmetry defined by the minor axes ofthecross-section of said diaphragm member;

said electromechanical converter means each cornprising:

a plurality of electromechanicallyeactive polarizable thin ceramicplates each of which has two oppositely-located substantially-parallelmajor planar surfaces and each of which is polarized to alternatelyexpand and contract along an axis substantially perpendicular to saidmajor planar surfaces in response to the application thereto of theintiuence of la uctuating electrical signal, the individual ceramicplates of said plurality of ceramic plates being successively stacked ontop of one another, with the next-successive ceramic plate in theresulting stack having its major planar surfaces in superimposedposition over i the major planar surfaces of the next-precedent ceramicplate to form an elongate stack of said ceramic plates;

insulator means, intermediate the respective longitudinal ends of saidelongate stack of ceramic plates and the diaphragm member associatedwith said electromechanical converter means, for electrically insulatingsaid elongate stack of ceramic plates from its associated diaphragmmember;

said stack of ceramic plates as supplemented by said insulator meansbeing of greater length than the natural undeformed inside dimensionmeasured along the major-axis of an elliptical cross-section of saiddiaphragm member will accommodate, so that placement of said stack ofceramic plates, as supplemented by said insulator means, within itsassociated diaphragm member necessitates mechanical deformation of thenatural cross-sectional shape of said diaphragm member to elongate itscross-sectional majoraxis dimension, said diaphragm member afterplacement therein of its associated stack of ceramic plates and theinsulator means accompanying said stack, imposing a compressive biasupon said stack of cera'mic plates in the direction of its longitudinalaxis because of the tendency of said diaphragm member to return to itsnormal, undistorted cross-sectional shape;

electrode means, operatively connected to each of said ceramic plateswhich form said elongate stack and also electrically connected to saidelectrically-conductive actuating means, for conveying to each of saidceramic plates the inuence of said uctuating electrical signal whichcauses said ceramic plates to alternately expand and contract.

3. The transducer of claim 2 wherein said electromechanical convertermeans further comprises mesh-like heat dissipating means connected toeach of said ceramic 1 plates for conducting heat away from said ceramicplates.

References Cited by the Examiner UNITED STATES PATENTS Hayes 340-9 XMason 340-8-6 Dranetz.

Barney 340-8 X CHESTER L. JUSTUS, Primary Examiner.

G. M. FlSHER, Assistant Examiner.

1. A COMPOSITE ELECTROMECHANICAL TRANSDUCER, ADAPTED TO TRANSMIT ORDETECT SOUND IN A LIQUID MEDIUM, AND HEREIN DEFINED IN TERMS OF ITSSOUND TRANSMISSION OPERATION COMPRISING IN COMBINATION: A PLURALITY OFOPEN-ENDED TUBULAR DIAPHRAGM MEMBERS OF IDENTICAL NON-CIRCULARCROSS-SECTIONS, EACH OF SAID TUBULAR DIAPHRAGM MEMBERS BEING ADAPTED TOVIBRATE IN THE FLEXURAL MODE OF VIBRATION FOR TRANSMITTING SOUND INTOSAID LIQUID MEDIUM AND SAID PLURALITY OF TUBULAR DIAPHRAGM MEMBERS BEINGARRANGED IN A LINEAR SERIES WHEREBY DIAPHRAGM MEMBERS FORM ANINTEGRALLY-OPERATIVE TUBULAR SOUND-TRANSMITTING MEANS ADAPTED TOTRANSMIT SOUND INTO SAID LIQUID MEDIUM; ELECTRICALLY-ACTUABLEELECTROMECHANICAL CONVERTER MEANS, INDIVIDUAL TO AND DISPOSED WITHINEACH OF SAID DIAPHRAGM MEMBERS IN THRUST-TRANSMITTING RELATIONSHIPTHEREWITH AND VIBRATILE IN THE LONGITUDINAL MODE OF VIBRATION INRESPONSE TO AN ACTUATING FLUCTUATING ELECTRICAL SIGNAL, FOR DRIVING ITSASSOCIATED DIAPHRAGM MEMBER IN FLEXURAL VIBRATILE MOVEMENT IN RESPONSETO SAID FLUCTUATING ELECTRICAL SIGNAL; CLOSURE MEANS, CONNECTED TO EACHEND OF SAID TUBULAR SOUND-TRANSMITTING MEANS, FOR CLOSING OFF SAIDTUBULAR SOUND-TRANSMITTING MEANS FROM SAID LIQUID MEDIUM; MULTIPLESEALING MEANS FOR ENSURING A LIQUID-PROOF CONNECTION BETWEEN THEADJACENT DIAPHRAGM MEMBERS; ELECTRICALLY-CONDUCTIVE ACTUATING MEANS,CONNECTED TO EACH OF SAID ELECTROMECHANICAL CONVERTER MEANS AND ADAPTEDTO CONNECT TO AN EXTERNAL ELECTRICAL LEAD BEARING SAID FLUCTUATINGELECTRICAL SIGNS; RESTRAINING MEANS, CONNECTED TO SAID CLOSURE MEANS,FOR HOLDING AND MAINTAINING SAID CLOSURE MEANS, SAID PLURALITY OFDIAPHRAGM MEMBERS AND SAID SEALING MEANS IN ASSEMBLED COOPERATIONRELATIONSHIP WITH RESPECT TO EACH OTHER; SAID CONVERTER MEANS EACHCOMPRISING; A STACK OF ELECTROMECHANICALLY-ACTIVE ELEMENTS EACH OF WHICHIS ADAPTED TO ALTERNATELY EXPAND AND CONTRACT ALONG THE LONGITUDINALAXIS OF SAID STACK IN RESPONSE TO THE APPLICATION TO SAIDELECTROMECHANICALLY-ACTIVE ELEMENTS OF AN ELECTRIC SIGNAL OF FLUCTUATINGINTENSITY, THE LONGITUDINAL ENDS OF SAID STACK BEING INTRUST-TRANSMITTING RELATIONSHIP WITH ITS ASSOCIATED DIAPHRAGM MEMBER;ELECTRODE MEANS, OPERATIVELY INTERCONNECTING EACH OF SAIDELECTROMECHANICALLY-ACTIVE ELEMENTS TO SAID ELECTRICALLY-CONDUCTIVEACTUATING MEANS FOR BRINGING EACH OF SAID ELECTROMMECHANICALLY-ACTIVEELEMENTS UNDER THE OPERATIVE INFLUENCE OF THE ACTUATING FLUCTUATINGELECTRICAL SIGNAL CARRIED BY SAID ELECTRICALLY-CONDUCTIVE ACTUATINGMEANS; INSULATOR MEANS, INTERMEDIATE THE RESPECTIVE LONGITUDINAL ENDS OFSAID STACK OF ELECTROMECHANICALLY-ACTIVE ELEMENTS AND THE DIAPHRAGMMEMBERS AASSOCIATED THEREWITH, FOR ELECTRICALLY INSULATING SAID STACK OFELECTROMECHANICALLY-ACTIVE ELEMENTS FROM SAID ASSOCIATED DIAPHRAGMMEAMBER; AND HEAT DISSIPATING MEANS, CONNECTED TO EACH OF THEELECTROMECHANICALLY-ACTIVE ELEMENTS IN SAID STACK FOR CONDUCTING HEATAWAY FROM SAID ELECTROMECHANICALLY-ACTIVE ELEMENTS, SAIDHEAT-DISSIPATING MEANS, IN PART, CONSISTING OF WIRE MESH-LIKE STRUCTUREFOR ACCELERATING THE DISSIPATION OF HEAT AWAY FROM SAIDELECTROMECHANICALLY-ACTIVE ELEMENTS.